Photogeneration of Carbon Monoxide and of Hydrogen via Simultaneous Photochemical Reduction of Carbon Dioxide and Water by Visible‐Light Irradiation of Organic Solutions Containing Tris(2,2′‐bipyridine)ruthenium(II) and Cobalt(II) Species as Homogeneous Catalysts

CO and H 2 are photogenerated simultaneously by visible‐light irradiation of systems containing a photosensitizer , the [Ru(bpy) 3 ] 2+ complex, Co ( II ) species as homogeneous catalysts, which mediate CO 2 and H 2 O reduction by intermediate formation of Co(I), a tertiary amine as electron donor , which provides the electrons for the reduction, and an organic solvent which also facilitates dissolution of CO 2 . The efficiency of (CO + H 2 ) gas production and the selectivity CO/H 2 markedly depend upon the composition of the medium, the nature of the tertiary amine, the solvent, and the ligand of the Co ions. 2,9‐Dimethyl‐1,10‐phenanthroline is particularly effective in promoting CO and H 2 formation, giving a quantum yield of 7.7% in (CO + H 2 ) (1.2% for CO and 6.5% for H 2 ). The process consists of two catalytic cycles: a photocatalytic cycle for the Ru complex and a double dark reaction pathway for the Co species; oxidative and/or reductive quenching of the excited state of the photosensitizer lead to the formation of Co(I) species which reduce either CO 2 or H 2 O to CO or H 2 , respectively.